Patent GB-841204-A (GB)
Title: Apparatus for producing discrete pulses
IPC: G11B20/14
Filed: 1956-10-16
Abstract: 841,204. Pulse handling circuits. INTERNATIONAL BUSINESS MACHINES CORPORATION. Oct. 16, 1956 [Oct. 17, 1955], No. 31480/56. Class 40(6). [Also in Group XIX] Fig. 1 shows the reproducing apparatus in a magnetic NRZ (non-return to zero) recording system in which a train of positive and negative pulses as shown in Fig. 2, 16 is recorded as a continuous wave-form of overlapping pulses Fig. 2, 17 and includes an interpreting device so that the pulses at the output 15 appear in a form suitable for handling in a digital computer. The signal recorded on the magnetic device, which is shown as a drum 1 in Fig. 1, passes a reproducing head or transducer 4 thus producing a signal similar to the first differential of the recorded wave-form as shown in Fig. 2, 21. This signal is integrated in unit 6 to produce wave-form Fig. 2, 22 and applied to full wave rectifier 7 the output of which Fig. 2, 23 has a ripple component Fig. 2, 24 which is extracted by band-pass filter 8 and which has one cycle corresponding to each of the original pulses of the recorded waveform. The ripple component controls a pulse generator 9 to produce positive pulses at output 10 and negative at output 11 which are applied to gate 14 which is controlled by the waveform Fig. 2, 25 produced from waveform Fig. 2, 22 by amplification and limiting in unit 12. Thus gate 14 transmits to the output a train of separate positive and negative pulses representing the stored binary information. Fig. 3 shows an interpreting circuit in which the output waveform from reproducing head 5 is amplified and integrated by Miller integrator stage 28 the output from which is amplified and limited by stages 40, 41, 42 to produce a waveform Fig. 2, 25 which controls the double diode gate 45, 46. The output of the integrator stage is applied via an inverter stage 29 to a control grid of tube 31 the non-inverted signals being applied to the control grid of cathode-coupled tube 33 so that the circuit 31, 33 comprises a full wave rectifier producing an output waveform Fig. 2, 23. The rectified signal is applied to an amplifier stage 35 having a parallel resonant anode circuit 36 tuned to the ripple component frequency thus acting as a band pass filter transmitting only the ripple frequency. Thus a waveform Fig. 2, 24 is applied to cathode follower stage 38 to trigger the conventional blocking oscillator 39 which produces positive and negative pulses respectively at outputs 10 and 11. These, are fed to diode gate 45, 46 which is controlled by the waveform Fig. 2, 25 to produce a train of positive and negative pulses on output 15 corresponding to the original stored information Fig. 2, 16. In a modification Fig. 4 (not shown) the reproducing head is centre tapped so that both an inverted and uninverted replica of the signal is produced at the two ends of the winding which are integrated and fed to full wave rectifier as previously described. In a further modification Fig. 5, the gate is controlled by a rectangular waveform produced from the output signal of the reproducing head via a two stable state trigger circuit use being made of the feature that portions of the signal Fig. 2, 20 which are produced following pulses of the opposite polarity has relatively larger amplitudes than do portions produced from pulses following those of the same polarity as shown in Fig. 6, 76. The larger amplitude pulses which may be either of positive or negative polarity are used to trigger a bistable circuit to produce an output Fig. 6, 79 or its inverse. The signal transmitted by rectifier 66, Fig. 6, 80 has a ripple component Fig. 6, 81 which is transmitted to gate 68 and appears at the output 69 whenever stage 63 is in its first operating state and transmitted to terminal 70 when stage 63 is in its second state. The outputs at 69 and 70 from the gate are used to control generators 71, 73 to produce positive and negative pulses respectively at outputs 72, 74. Fig. 7 shows a circuit for carrying out the functions of Fig. 5 in which one output from reproducing head 5 is applied via inverter stage 85 to one trigger input of bistable circuit 88, 89 which in conjunction with biased rectifiers 90, 91 is triggered only by the large amplitude pulses of either negative or positive polarity which indicate a change in the polarity of the pulses present in the original reproduced signal. An output from the reproducing head 5 is applied through amplifier stage 94 to a full wave bridge rectifier 101, 102, 103, 100 which is biased by current produced from flip-flop 88, 89 to invert the phase of selected portions of a signal between windings 96, 98 corresponding to the signal provided at head 5. The ripple component is extracted by a tuned circuit comprising transformer secondary winding 104 is amplified in stage 105 which has a further parallel tuned anode circuit 106 also tuned to the ripple frequency. This component is then transmitted to the tubes 107, 108 which form part of a gate circuit for transmitting the ripple component either to lead 69 or 70 in dependence on the state in which the trigger circuit 88, 89 is operating. The output from the gate triggers pulse generators 109, 110 to produce trains of positive and negative pulses at their output terminals corresponding to the original reproduced signal. In a modification Fig. 8 a single two-stable-state trigger circuit also performs the function of the biased rectifier of Fig. 5. Reproducer head winding 5 producing both a direct and inverted version of the waveform, Fig. 6, 76. Which signals are applied to bistable circuit 115, 116 which is triggered only by the larger amplitude positive or negative signals which indicate a change in the polarity of pulses in the original signal. Thus the cathode potential of tubes 115, 116 has a waveform Fig. 6, 80 the ripple component of which Fig. 6, 81 is extracted by parallel resonant circuit 121 which is differentiated by circuit 123, 124 amplified in stage 125 which also clips alternate half cycles of the waveform and due to the action of network 127, 128, 129, 130 a train of short positive pulses is produced across resistor 130 one occurring for each recorded magnetic pulse of either polarity Triodes 131, 132 comprise a gate controlled by the output of bistable circuit 115, 116 so that each time a positive pulse is produced across resistor 130 a pulse is produced in the anode of the conductive tube of tubes 131, 132. A positive pulse is thus produced at lead 133 for each positive recorded pulse and a positive pulse at lead 134 for each recorded negative pulse. These trigger pulse generator mono-stable flip-flops 135, 137 to produce a train of positive and negative pulses Fig. 6, 75 representing the stored information at outputs 136. In a further modification Fig. 9 (not shown) a single bistable trigger circuit performs the functions of the trigger circuit and bias rectifier of Fig. 5 and also the gating function.